Special equipment: a turkey injector, meat thermometer, oil-less fryer and roasting pan
Combine the mayonnaise, milk, parsley, dill, vinegar, salt, garlic powder, garlic salt and pepper in a blender and process until smooth, about 2 minutes. Measure out 3/4 cup of the ranch dressing and set the remainder aside for serving at the table.
Fill a turkey injector with the 3/4 cup ranch dressing and inject 2 tablespoons of the dressing into each thigh of the turkey, 1 tablespoon into each drumstick and 3 tablespoons into each breast. Let the turkey stand at room temperature for 30 minute to let the dressing soak into the meat. Discard any of the unused ranch dressing in the injector (it has been in contact with the raw turkey).
Mix together the olive oil and melted butter in a small bowl. Brush the turkey with the oil mixture and then sprinkle with salt.
Preheat an oil-less fryer for cooking (alternatively, follow oven-roasting directions below). Place the turkey breast-side up in the fryer with the legs in the deepest part. Cook the turkey until a meat thermometer inserted in the thickest part of the breast reaches 160 degrees F, about 2 hours. (The breast cooks slower than the legs in the oil-less fryer; carryover cooking will cook it the rest of the way through.) Remove the basket insert with the turkey and let the bird rest at least 30 minutes over a roasting pan. Remove the turkey from the basket, carefully dislodging any parts of the turkey that are touching the basket so the skin does not tear. Carve the turkey and serve with the reserved ranch dressing or gravy.
Alternatively, roast the turkey in the oven: Preheat the oven to 350 degrees F. Inject the turkey with the dressing as directed above and set it in a roasting pan. Roast, basting every 30 minutes, until a meat thermometer inserted in the thigh reaches 160 degrees F, about 3 hours (the carryover cooking will cook it the rest of the way through). Transfer to a carving board and let rest 30 minutes before carving.